New dideoxy carbocyclic nucleosides inspired by the structure of the fermentation product neplanocin C were synthesized and evaluated for antitumor and antiviral activity. The epoxy oxygen of the [3.1.0]bicyclic system present in neplanocin C was replaced by carbon, thus generating a more robust fused cyclopropane system. The [3.1.0]bicyclic-containing carbocyclic nucleosides possess a rigid pseudosugar conformation in the northern hemisphere of the pseudorotation cycle as ascertained by NMR spectroscopy.